My first EOS was the EOS 650. Then came the EOS 7 with its excellent eye control AF. After that, I used EOS 10D, EOS 20D and EOS 50D. After the 50D, I got the the EOS-M, which was excellent, the EOS M6, which was laggy and therefore awful and the EOS M6 Mark 2, which is excellent again.
I own some not-so-great (by today's standards) EF lenses and many EF-M lenses. Here is the list of lenses which have EF-M mounts:
Canon EF-M 11-22mm f/4-5.6 IS STM
Canon EF-M 15-45mm f/3.5-6.3 IS STM
Canon EF-M 18-55mm f/3.5-5.6 IS STM
Viltrox 7,5mm f/2.8
Samyang 8mm f/2.8
Sigma 16mm f/1.4 DC DN | C
Canon EF-M 22mm f/2 STM
Canon EF-M 28mm f/3.5 Macro IS STM
Canon EF-M 32mm f/1.4 STM
Kamlan 50mm f/1.1
Kamlan 50mm f/1.1 Mark 2
I mostly use the following lenses:
Samyang 8mm f/2.8
Canon EF-M 11-22mm f/4-5.6 IS STM
Sigma 16mm f/1.4 DC DN | C
Canon EF-M 22mm f/2 STM
Canon EF-M 28mm f/3.5 Macro IS STM
Canon EF-M 32mm f/1.4 STM
Kamlan 50mm f/1.1 Mark 2
If Canon decided to end the M-Line, all these lenses would be rendered useless in a long term. That doesn't seem acceptable to me, at least from the environmental perspective.
Those M-lenses are really good by standards of my old EF lenses and are sufficient for my needs. I might sell the ones I use less, but so far I haven't had the time or motivation to do that. Selling the whole system is even less interesting to me: Selling things one by one is an annoying process and selling the whole lot of stuff at once usually means losing more money than when selling one by one. So I I don't like both variants. Which is kind of stupid, of course, but that doesn't hurt either.
I would like to continue using my EF-M lens collection for as long as possible because with the original EOS-M or EOS-M6 MK2 (instead of the awful M6), they give me joy of photography. I'm not interested enough by the current innovations of the R system. Selling everything and starting a new camera and lens collection is not my focus right now. It just costs too much time and effort and many items are not even readily available to buy. On the other hand, there are not so many lenses that I need to change, and a new, more capable body is never a bad idea. Nevertheless, I just don't want to give up my tried and true leneses and a system I love to use. It's more of a feeling, of course.
Note: My current focus is photography, not videography, although I consider videography a very nice addon. I've done much of my YouTube work using iPhones or a Panasonic Camcorder, which have been way more reliable and suitable for fast and continuous video work than any Canon I've seen, except the C-Series.
The compactness of the camera is a very nice touch of the M-System, but it's not extremely important for me. I like to use my M6 MK2 with a Smallrig wood handle arca swiss bracket on, after all. The small size of the lenses on the other hand, is a very good and important feature. I like to use prime lenses and being able to comfortably carry many relatively bright primes with me is a thing I'm now used to. This would not be possible with a full frame system with it's way larger fast primes.
So would I ever buy an RF body? And if so, will it be APS-C or FF?
If Canon offered a "speed booster" converter from EF-M to RF, I would consider buying two RF bodys in the future. One small APS-C body and one full frame top spec body with some fancy, expensive lenses. The prerequisite of a speed booster offering from Canon (for the APS-C RF body at least, better for all RF bodies) is important, not because I consitder it very useful for delivering top notch results (it is not), but because I would feel respected by Canon in my (perhaps not very practical) choice of not selling my lenses. Otherwise, I'm just not interested enough to invest in a new system. I would also buy new M bodies if Canon offered something new, like IBIS.
I just don't like throwing everything out and starting over. A slow transition seems fine. In the end, I kind of (mostly?) switched from EF to M. Maybe because I could continue to use my familiar lenses with the new camera?